Steel-belted radial ply tires with 0° textile cap band

ABSTRACT

A steel-belted radial ply tire construction characterized by improved uniformity and resistance to ply separation, and a method of manufacturing such tires in non-segmented molds, are disclosed. In the finished tire, a cap band having at least one layer of rubberized tire cords of synthetic filamentary textile material is disposed in direct surrounding relation to the radially outermost belt ply of bias-angled steel cords, the cap band having a width equal to or greater than the width of the belt, with the cords in the cap band being disposed parallel to one another and to the median equatorial plane of the tire, i.e., at an essentially 0° bias angle. The cords in the cap band are prestressed, due to their having been stretched about 1 to 5% in the manufacturing operation during the final expansion of the tire into the mold contours under high internal pressure, so as to exert a stability and uniformity-enhancing compressive stress on the underlying belt. The cap band also serves, during the final in-mold expansion of the tire during the manufacturing process, to ensure uniform pantographing of the steel cords in the belt plies to their desired bias angles. This abstract is not to be taken either as a complete exposition or as a limitation of the present invention, however, the full nature and extent of the invention being discernible only by reference to and from the entire disclosure.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a division of copending U.S. patent application Ser.No. 334,198, filed Feb. 21, 1973, entitled "Steel Belted Radial PlyTires with 0° Textile Cap Band" by Robert H. Snyder and assigned to theassignee of the present invention now U.S. Pat. No. 3,850,219. Ser. No.334,198 is a continuation-in-part of U.S. patent application Ser. No.281,890, filed Aug. 18, 1972, and now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to pneumatic tires for vehicles and moreparticularly to belted radial ply tires of the type having a cap bandoverlying the belt thereof.

The expressions "radial tires" and "radial ply tires" as commonly usedin the pneumatic tire art may be said to include various tireconstructions having a carcass or body comprising one or morereinforcement plies of rubberized tire cords extending from bead to beadwherein the cords in each ply are substantially radial in orientation,i.e., the cords are oriented substantially normal to the beads and tothe crown centerline of the tire. In a mono-ply radial tire the carcassor body cords normally have a 90° bias angle, i.e., in the unshapedcarcass they extend perpendicular to the planes of the beads. In atwo-ply radial tire, the cords in each body ply are usually oriented atoppositely disposed small angles of up to 10° with respect to theperpendicular to the bead planes, in which case the respective bodyplies are said to have oppositely disposed bias angles of 80° or greater(but less than 90°). In four-ply or heavier radial ply tireconstructions similar opposed orientation of the cords in successivebody plies is usually employed. All of these body or carcassconstructions are contemplated within the scope and meaning of theexpressions "radial" and "substantially radial" as used herein.

Radial tires are generally constructed with a breaker or belt interposedbetween the crown region of the carcass and the tread for reinforcingthe latter, such breaker being comprised of one or more layers or pliesof tire cords or cables which are generally inextensible, i.e., made ofsuch materials as metallic wires, glass fiber, rayon, etc. In a mono-plybelt, the cords or cables have a relatively low bias angle of 0°, i.e.,they are oriented substantially parallel to the planes of the beads andto the median equatorial plane, or crown center line, of the tire. Ifthe belt is of a multi-ply construction, similar but opposed low biasorientations of the cords or cables generally at angles ranging up toabout 25°-30° or so with respect to the median equatorial plane of thetire are employed in successive plies.

It is known that many types of tires, especially radial ply carcasstires in which, as above stated, the tread is reinforced by a belt orbreaker composed of superposed, mutually crossed, rubberized plies ofparallel, essentially inextensible cords or cables, often fail at highspeeds because separations occur in the shoulder zones of the tireswhere the edges of the belt plies are located. Such ply separations aredue to the cord ends at the edges of the belt plies becoming detachedfrom the surrounding rubber under the combined effects of centrifugalforce acting on the tire, flexing of the tire and heat build-up in thetire. This result is made even more likely by the fact that the cords orcables in the belt plies, being disposed obliquely to the medianequatorial plane of the tire by virtue of said plies being cut obliquelywith respect to the longitudinal direction of the cords or cablestherein, have a natural tendency to spread apart at their cut ends. Theedges of the belt thus constitute zones where the cut and free ends ofthe reinforcing elements, i.e., the cords or cables, by friction and bycutting, cause breaks both in the carcass plies and in the rubber of thetire.

Belted radial ply tires of the type presently known in the art arefurther subject to the disadvantage that they tend to snake or squirm ina direction orthogonal to the direction of motion of the vehicle onwhich they are mounted, which results in excessive tire wear, prematuretire failure and excessive vibration. This snaking of tires cured intwo-piece or non-segmental molds of the types known to the art, appearsto be due, at least in part, to the fact that such tires must undergotheir final expansion into the full mold contours after being insertedin the molds. During such expansion of a tire in the mold, the cords orcables of said belts pivot relative to each other, i.e. they pantographto a lower bias angle than that at which the cords or cables areoriginally oriented in the belt plies during the building operation. Dueto stresses within the tire and the uneven expansion of various portionsof the tire, however, the cords or cables tend to pantographnon-uniformly, and it is the resultant non-uniform cord orientationswhich cause the aforementioned disadvantageous snaking.

It might be noted that belted radial ply tires having an additional bandof textile cords overlying the belt are known in the art. For example,French Pat. No. 1,416,538 discloses the use of such a band having asingle ply therein, the cords of which may be oriented at any desiredangle from 0° to 90° to the median equatorial plane of the tire andwhich serves to shield the belt cords from moisture. This patent doesnot, however, disclose a structure which overcomes either the problem oftire distortion and ply separation at high speeds, or the problem ofnon-uniform pantographing of the cords or cables of the belt pliesduring tire manufacturing.

Another example of a belted radial ply tire utilizing an added band oftextile cords over the belt is illustrated in U.S. Pat. No. 3,503,432.In that tire, the added band is made of heat-shrinkable nylon cords, andthe shrinkage stresses developed in such nylon cords are utilized tocondition the band to apply a compressive stress to the underlying beltplies and to absorb some of the stresses present in the tire duringoperation. The breaker and cap band portion of the tire must, however,be cured in a segmental mold and thus is already at its desired finaldiameter when being placed into the mold. Since there is no furtherin-mold expansion, therefore, the patent does not teach a solution to,nor even have to face the problem of, non-uniform pantographing of thebelt cords during tire manufacture.

SUMMARY OF THE INVENTION

It is, therefore, an important object of the present invention toprovide an improved belted pneumatic tire construction and a method ofmaking tires having such a construction, by means of which the aforesaiddrawbacks and disadvantages may be most efficaciously avoided.

It is a further object of this invention to provide a belted radial plytire characterized by a high degree of uniformity and resistance to beltply separation.

Generally speaking, the objectives of the present invention are attainedby the provision of a belted pneumatic tire for vehicle wheels, the tireincluding at least two belt plies of metal cords between the tread andthe crown region of the carcass, the cords extending parallel to oneanother in each layer and being crossed with respect to the cords ofeach next adjacent layer, said cords being inclined at an angle ofbetween 16° and 30° with respect to the median equatorial plane of thetire, each said ply having a width approximately equal to that of thetread, and a cap band having at least one layer of textile cordspositioned beneath the tread and radially outward with respect to saidmetal cord belt plies, said cap band having a width equal to or greaterthan that of the belt plies and being formed by at least one layer ofcords extending parallel to one another and to said median equatorialplane of the tire, said textile cords being longitudinally extensiblewhen stressed and in the finished tire being elongated between about 1%and 5% from their unstressed state, said textile cords thereby beingprestressed to exert a compressive stress on the underlying belt pliesfor enhancing uniformity of geometrical and rolling properties of thetire and for restraining belt ply separation due to radially outwardmovement of said metal cords under centrifugal forces.

The use of the said cap band also enables the steel-belted radial plytires of the present invention to be cured in a two-piece or clam shellor non-segmental mold rather than in a segmental mold as has heretoforebeen necessary. This advantage is due to the fact that, even though theraw preshaped tire as inserted into the mold is somewhat smaller thanthe mold and must undergo a final expansion of between about 1 and 5%upon being forced into the full mold contours by the high internalpressure of the curing fluid, the cap band ensures that thepantographing of the bias-angled steel belt cords to their desired finalangle of between about 16° and 30° to the median equatorial plane willtake place in as uniform a manner as possible so as to lead to asuniform a final tire as possible, thereby diminishing the snaking of thetire while it is in service.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects and features of the present inventionwill be more clearly understood from the following detailed descriptionthereof when read in conjunction with the accompanying drawings, inwhich:

FIG. 1 is a partially sectioned perspective view of a belted radial plytire having a cap band according to one embodiment of the presentinvention;

FIG. 2 is a reduced scale schematic side view of the cap bandillustrated in FIG. 1;

FIG. 3 is a schematic side view of a second embodiment of a cap band fora belted radial ply tire according to the invention; and

FIG. 4 is a schematic view of a tire and mold illustrating the finalexpansion of a tire within the mold according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to FIG. 1 there is illustrated a tire 1 comprising tworadial or substantially radial superposed carcass plies 3 and 5,sidewalls 7 and 9 overlying the respective lateral regions of thecarcass and terminating at their radially inwardmost edges in a pair ofbeads 11 and 13, a tread 15 overlying the crown region of the carcassand adjoining the sidewalls 7 and 9 at their radially outwardmostregions, i.e., in the area of shoulders 17 and 19 of the tire, two beltbreaker plies 21 and 23 superposed one on the other and both interposedbetween the crown region of the carcass and the tread for reinforcingthe latter, a fluid-impervious liner 25 radially inward of carcass orbody ply 3 and extending from bead 11 to bead 13, and a single layer capband 27 interposed between radially outwardmost belt ply 23 and tread15.

Describing the cord ply components of the tire in a radially outwarddirection, body plies 3 and 5 are layers of rubberized cords or cablesmade of any suitable natural or synthetic fiber such as nylon, rayon,polyester, metal wire, glass fiber, etc., and each of the body plies 3and 5 extends from bead to bead. In the body plies illustrated, thecords in each body ply are oriented at oppositely disposed small andnormally equal angles of up to about 10° with respect to true radialplanes, and thus the respective body plies have opposite bias angles ofbetween 80° and 90° with respect to the median equatorial ormid-circumferential plane. The belt plies 21 and 23 are layers ofrubberized, parallel, metallic reinforcing elements, preferably steel,which may be either lamelliform, i.e., in the form of flat strips orbands with rounded edges, or filiform, i.e., in the form of generallyround wires or cables, and these plies are approximately equal in widthto the tread 15. The steel reinforcing elements in each ply are orientedat a substantial bias angle of between about 16° and 30° to the medianequatorial plane of the tire.

The cap band 27 which is superposed on the radially outwardmost belt ply23 and is therefore in direct contact with the ply 23, is a rubberizedlayer of a plurality of parallel cords or cables of a non-metallictextile material, for example rayon, nylon, polyester, etc., and saidtextile cord or cables are oriented at a substantially 0° bias angle,i.e., they are substantially parallel to the median equatorial plane ofthe tire. Cap band 27 is at least as wide as the widest one of said beltplies 21 and 23 and preferably between about 20 and 60 millimeters widerthan said belt plies, i.e., 10 to 30 mm wider on each side of the belt.

Turning now to FIG. 2, there is schematically illustrated a reducedscale side view of cap band 27 shown in FIG. 1. It will be noted thatcap band 27 comprises the aforementioned single layer of rubberizedtextile material and that there is some selected overlap of, andcorresponding adhesion of the marginal portion between, the ends 27a and27b of the band 27. The function of the splice overlap and adhesion ofthe marginal portions of cap band 27 to one another is to minimizeslippage of the band ends 27a and 27b relative to one another duringexpansion of the tire into the mold of a vulcanization press.Notwithstanding the overlapping of ends 27a and 27b, however, it hasbeen found that the use of a single layer cap band results in a moderateamount of slippage in the splice overlap thereof during the in-moldexpansion. This slippage causes tread 15 to stretch non-uniformly in thearea overlying the splice overlap and results in a depression across thetread from shoulder 17 to shoulder 19. It may also cause one or more ofthe steel breaker plies 23 and 21 to pantograph in a slightlynon-uniform manner in the area of the cap band splice overlap, withattendant snaking problems. Such slippage can also result inout-of-roundness of the tire in the slippage area, and in the narrowingof one or more of the steel breaker plies in such area.

Turning now to FIG. 3, there is illustrated a schematic side view of asecond embodiment of a cap band 28 according to the invention, which capband may advantageously be substituted for the cap band of the tireshown in FIG. 1 when it is desired to further minimize slippage at themarginal portions of the cap band during the final in-mold expansion ofthe tire. The cap band 28 illustrated in FIG. 3 is constituted by tworubberized layers of parallel ply textile cords or cables formed from asingle length of textile material which has been spirally wrapped slightmore than twice about the crown portion of the tire. In this arrangementthe band ends 28a and 28b define a region of overlap 29 wherein theouter marginal portion of the band and the inner marginal portion of theband adhere to opposite sides of a continuous central layer of the band.The region of overlap 29 is thus reinforced by the continuous centrallayer of the band and slippage of ends 28a and 28b relative to oneanother is diminished. The tread 15 will therefore stretch moreuniformly above the region of overlap and the belt ply 23 will narrowless under the region of overlap in the FIG. 3 embodiment than will bethe case where the single layer cap band of FIG. 2 is utilized. It ishere appropriate to note that it is desired that the cap band exert thesame selected amount of compressive stress on the underlying belt pliesirrespective of whether a single layer or a two layer cap band is beingutilized. To achieve this end it has been found advantageous, whenemploying a two layer cap band having cords or cables of similarphysical properties to utilize only one-half as many parallel textilecords or cables per transverse measure as when a single layer cap bandis employed. For example, if, when a single layer cap band is utilized,it has been found that the appropriate compressive stress is applied tothe underlying belt plies when the cap band is constituted by 24 cords(or ends) per transverse inch, then a band constituted by 12 cords pertransverse inch is appropriate when a two layer spiral wound cap band isused. Alternatively, the physical properties of the cords or cables inthe two layer cap band may be so chosen as to require various othernumbers of cord ends per inch, such selection being well within thenormal skill of the art.

Turning now to FIG. 4, there is schematically illustrated anon-segmental or two-piece mold 40 of a type well known in the art, sucha mold being, of course, one which has a continuous tread groove formingperiphery and is thus incapable of radial expansion or contraction. Sucha mold in essence has a lower mold section 42 and an upper mold section(not shown). The inner mold surfaces carry a plurality of ridges or likeprotrusions, indicated in FIG. 2 by the dot-dash line 44, to form thegrooves in the tire tread. Since as above stated, this mold is of thenon-segmental type, it will be clear that the preshaped tire 46,commonly referred to by those in the art as a "second stage carcass,"will have to have an outer radius R₁ somewhat smaller than the innerradius of the envelope of the groove-forming protrusions so that saidsecond stage carcass may be easily inserted into mold 40. The secondstage carcass thus is somewhat smaller than it will ultimately be whenfully expanded into the mold. As shown, the mold has an inner radius R₂which is between about 1 and 5% greater than radius R₁.

After insertion of the preshaped tire 46 into mold 40, with the beads 48properly seated, the mold is closed and high pressure heating fluid,e.g., steam or hot water, is admitted into the curing bag or bladder(not shown) to expand the same and therewith the carcass 46 in aradially outward direction until the peripheral surface 50, i.e., thetread, of said carcass contacts the inner surface of the mold.

It is during this final in-mold expansion of the tire than anotheradvantage is obtained by using a cap band constituted by at least asingle layer of cords which are longitudinally extensible and which areoriented at a substantially 0° angle with respect to the medianequatorial plane of the tire. It should be noted that in the manufactureof a belted tire as herein contemplated, the carcass is built insubstantially flat or cylindrical form and is then shaped to itstoroidal form, whereupon the belt plies, the cap band in an unstressedcondition, and the overlying tread rubber are applied to the crownregion of the shaped carcass to complete the raw tire. The latter will,of course, as previously stated, have an outer diameter somewhat smallerthan the inner mold surface diameter. Accordingly, there will be somedegree of pantographing of the belt cords, which may be non-uniform ifnot properly regulated, during the final expansion of the tire in themold. During that final expansion of the tire, however, the cords of thecap band will be also longitudinally extended in the same degree, i.e.,between about 1 and 5% and preferably between about 1 and 3% of theirinitial unstressed length, and by virtue of their juxtaposition to thebelt plies will exert a restraining force on the metal cords of the beltplies so as to ensure that the belt cords will pantograph as uniformlyas possible. The significance of this feature is that by minimizing thetendency of the belt cords to pantograph non-uniformly, it becomespossible to avoid an ultimate tire construction that may be sufficientlynon-uniform to cause the tire, when in service, to snake excessively andpossibly suffer premature failure.

After the mold cycle is completed, the still hot tire is removed fromthe press and mounted on a post inflation chuck where it is inflated toa pressure of between about 30 and 50 p.s.i. until the tire issufficiently cool to permit further handling. The post inflationtreatment not only ensures that the tire will be maintained in a uniformconfiguration during the cooling period, but also that the cords of capband 27 will retain the prestress applied thereto by their longitudinalextension during the final in-mold expansion of the tire. Accordingly,the cap band cords will exert the desired radially inward compressivestress on the belt plies of the tire even after the end of the postinflation treatment, thereby actively aiding in maintaining the tire inas uniform a condition as possible. The prestressing of the cap bandcords also affords a number of other benefits. For example, at highspeeds, standing waves may be set up within a belted tire due todistortions of the belt, which could cause premature tire deterioration.The cap band 27, by virtue of its compressive action, tends to avoidthis problem. The cap band will also minimize the risk of belt plyseparation which could occur at high speeds due to the effects ofcentrifugal forces if no such band were present. It is for this purpose,of course, that the cap band must have a width at least as great as thewidest of the belt plies and preferably somewhat wider, so that the capband cords will continuously urge the lateral edges of said belt pliestoward the carcass.

Although the foregoing description has described belt plies 21 and 23primarily as utilizing steel or like metal cords or cables as thereinforcing elements, it will be understood that the principles of theinvention are applicable to belts having cords of other high modulusmaterials, such as rayon, glass fiber, Fiber B, and the like,incorporated therein.

It will be understood that the foregoing description of the preferredembodiment of the present invention is for purposes of illustrationonly, and that the various structural and operational features as hereindisclosed are susceptible to a number of modifications and changes noneof which entail any departure from the spirit and scope of the presentinvention as defined in the hereto appended claims.

Having thus described the invention, what is claimed and desired to beprotected by Letters Patent is:
 1. In the method of making a radial plytire having between the crown region of the carcass thereof and thesurrounding tread a belt composed of at least two superposed plies ofhigh modulus belt cords oriented at an angle of between about 16° andabout 30° with respect to the median equatorial plane of the tire, withthe belt cords being parallel to each other within each belt ply andbeing crossed with respect to cords in each next adjacent belt ply,wherein the carcass is built in substantially cylindrical form, saidcarcass is then shaped to toroidal form, and the belt and the tread arethereafter applied to the crown region of the shaped carcass preparatoryto the placing of the raw tire into the mold for curing; the improvementcomprising the steps of incorporating between the radially outwardmostbelt ply and the tread during the building operation a cap band havingat least one layer which is at least as wide as the widest of said beltplies and has incorporated therein a plurality of textile cords orientedsubstantially parallel to one another and to said median equatorialplane, with said cap band in direct contact with the radiallyoutwardmost one of said belt plies, placing said raw tire into atwo-piece mold, and applying internal fluid pressure to said raw tireupon closing of the mold for expanding said raw tire fully into the moldcontours and concurrently stressing said textile cords in said cap bandto elongate by between about 1% and about 5% from their unstressedcondition, said textile cords thereby exerting a restraining force onsaid belt plies to ensure substantially uniform pantographing of saidbelt cords during said expansion.
 2. The method of claim 1, wherein saidraw tire is expanded to elongate said textile cords between about 1% andabout 3% from their unstressed condition.
 3. The method of claim 1,wherein said raw tire is expanded to elongate said textile cords about3% from their unstressed condition.
 4. The method of claim 1, whereinsaid cap band comprises a single layer of textile cords.
 5. The methodof claim 1, wherein said cap band comprises two layers of textile cords,formed from a single length of spirally wrapped textile material,thetextile cords in each of said layers being oriented substantiallyparallel to one another and to said median equatorial plane and beingstressed to elongate them by between about 1% and about 5% from theirunstressed condition.